Lightning's glow: AC or DC?

[otomanb]

Usually all of us observe thundering light at rainy day. A light is produced. Is that a.c or d.c
Thanks

 

[sophiecentaur]

The 'net' discharge is just one way because a positively charged object is discharging to a negatively charged object. but it is in the form of a pulse, which consists of a whole set of frequencies - going up to hundreds of MHz (hence the RF interference)- in addition to the DC bit.

 

[Airbag79]

Usually all of us observe thundering light at rainy day. A light is produced. Is that a.c or d.c
Thanks

The "light" produced is plasma, not current. So it is neither AC or DC.

 

[Ken Freeman]

My understanding is that charge is moving through the atmosphere, therefore there is a current. It creates a plasma channel out of the air because of the very high current density, and hence a lot of Joule heating of the channel. But really, the mechanism of plasma formation probably needs a bit more explanation than I'm offering.

 

[Bob S]

Visible light is about 10¹⁵ Hz (about 0.5 micron wavelength).

Bob S

 

[karthicknar]

As mentioned in this post

The 'net' discharge is just one way because a positively charged object is discharging to a negatively charged object. but it is in the form of a pulse, which consists of a whole set of frequencies - going up to hundreds of MHz (hence the RF interference)- in addition to the DC bit.

lightning is just discharge of charges due to electrical breakdown of dielectric material (air) between them. But the flow of current is unidirectional even though it is in the form of a pulse. So it seems for me to say more logical that the lightning discharge is some form of short term directional current (DC).

 

[Ken Freeman]

Visible light is about 10¹⁵ Hz (about 0.5 micron wavelength).

Bob S

Yes, that's true. Lightning is a very brief transient signal, so while it has a strong DC component, there is a lot of energy at components with elevated frequency, viewed from a frequency domain point of view. But the reason it glows is the emission of energy at the 10^15 hertz range. This is due to the non-linearity of air as an ionized conductor of electricity. Plasma currents are typically very noisy due to the complex and very energetic dynamics of the excited molecules and their electronic structures. Some of the resonances due to this electronic excitation are in the visible range, and hence are visible.

So while lightning is a current transient that is essentially unipolar, it excites charge carriers with spectral energy with an extremely broad bandwidth. Spectral lines are produced that are within the visible spectrum.